Polyurethanes (PUs) consist of polymers composed of a chain of organic units joined by carbamate (urethane) links resulting from the reaction between a hydroxyl group and an isocyanate group as follows:

Industrially, polyurethane polymers are usually formed by reacting an isocyanate with a polyol where both the isocyanate and the polyol contain on average two or more functional groups per molecule. The equation below represents an example of a reaction to produce a polyurethane where a Methylene Diphenyl Diisocyanate (MDI) is reacted with ethylene glycol.

PUs can be produced in many different forms from very low density foams to high performance composites and can thus be used in a multitude of applications. Examples of applications include flexible high-resilience foam seating, rigid foam insulation panels, electrical potting compounds, high performance adhesives, surface coatings, packaging, surface sealants and synthetic fibers to name just a few.
PU foams are usually produced by reacting a resin containing a combination of at least one polyol, surfactant(s), catalyst(s) and blowing agent(s) with an isocyanate containing two or more isocyanate groups.
The polyols used in the production of PUs generally originates from petroleum products. However, due to environmental issues, more and more industrial processes nowadays try to replace petroleum products by “greener” products originated from the biomass. Lignin, which is a polyol biopolymer which can be easily extracted from food-grade and non-food grade biomass, such as agricultural waste or biomass from forests, is seen as a good candidate to replace, at least in part, polyols resulting from petroleum products.
Lignin is the second most abundant biopolymer on earth, after cellulose, and a known by-product of the pulp and paper industry. Physical and chemical properties of lignin depend on wood species, botanic region, and extraction and isolation processes. The use of lignin is attractive because it is less expensive than polyols and may create a smaller environmental footprint.
Lignin has previously been used in the production of PU foams. For example, PU foams have been produced by adding lignin as an organic charge in the polyol-isocyanate mixture. In another process, lignin was dispersed in the polyol containing resin prior to mixing the resin with the isocyanate. Another process for the production of PU foams involved chemically modifying the lignin before mixing with the resin and then with the isocyanate. However, these processes present drawbacks, including for example a high cost production or a cost superior to petroleum derived raw materials, difficulties to regulate the viscosity and/or difficulties to prepare PUs containing relatively high quantities of lignin.
In light of the aforementioned, there is thus a need for a new process for producing polyurethanes which is economic and environmentally friendly.
There is a need for a new process for producing lignin based polyurethane products limiting the above mentioned difficulties observed in known polyurethane production processes.